If the number 42573 * is exactly divisible by 72, then the minimum value of * is:

Question: If the number 42573 * is exactly divisible by 72, then the minimum value of * is:

[A].

4

[B].

5

[C].

6

[D].

7

Answer: Option C

Explanation:

72 = 9 x8, where 9 and 8 are co-prime.

The minimum value of x for which 73x for which 73x is divisible by 8 is, x = 6.

Sum of digits in 425736 = (4 + 2 + 5 + 7 + 3 + 6) = 27, which is divisible by 9.

Required value of * is 6.

What is the unit digit in 7105 ?

Question:
What is the unit digit in 7105 ?

[A].

1

[B].

5

[C].

7

[D].

9

Answer: Option C

Explanation:

Unit digit in 7105 = Unit digit in [ (74)26 x 7 ]

But, unit digit in (74)26 = 1

Unit digit in 7105 = (1 x 7) = 7

397 x 397 + 104 x 104 + 2 x 397 x 104 = ?

Question:
397 x 397 + 104 x 104 + 2 x 397 x 104 = ?

[A].

250001

[B].

251001

[C].

260101

[D].

261001

Answer: Option B

Explanation:

Given Exp. = (397)2 + (104)2 + 2 x 397 x 104
= (397 + 104)2
= (501)2 = (500 + 1)2
= (5002) + (1)2 + (2 x 500 x 1)
= 250000 + 1 + 1000
= 251001